Facet‐Dependent Water Inhibition of Alkanol Dehydration on TiO ₂ via Distinct Water–Alkanol Complexes

Abstract

ABSTRACT Water is ubiquitous in biomass‐derived feeds, yet its molecular impact on oxygen‐elimination reactions remains poorly understood, particularly for catalysts exposing different facets. Here, we utilize well‐defined TiO 2 nanocrystals with dominant (101) and (001) facets to reveal a pronounced facet‐dependent effect of water, where inhibition for dehydration of isopropanol (IPA) on the TiO 2 (001) surface is about four times more severe than TiO 2 (101). Through a combination of in situ solid state NMR, in situ infrared spectroscopy, kinetics studies, and theoretical calculations, we demonstrate that this disparity arises from the formation of distinct alkanol‐water complex intermediates. On TiO 2 (001), IPA undergoes dissociative adsorption to form an isopropoxide‐H 2 O complex that readily drives the surface into a complex‐dominated regime. This pathway increases the activation barrier for C–H cleavage by 40 kJ mol −1 by inducing a disordered transition state. In contrast, TiO 2 (101) favors molecular IPA adsorption with weak hydrogen bonding to water, resulting in a smaller complex formation constant and a much smaller activation barrier increase (25 kJ mol −1 ). By quantitatively linking facet‐dependent complex coverage to transition‐state destabilization, this work moves beyond simple site‐blocking models and provides a conceptual framework for designing catalysts that remain active in water‐containing environments.